1. Field of the Invention
The present invention relates to an electrophoresis display device, and particularly relates to an active matrix type electrophoresis display device having a thin film transistor (hereinafter, referred to as TFT) prepared on an insulating material and using an electrophoresis element as a pixel.
2. Description of Related Art
In SID'01 (Society of Information Displays—2001) held in San Jose in June, 2001, E Ink, Corp. has published an electrophoresis display device, and attracted the great deal of attention. The electrophoresis display device published by E Ink Inc. is a display device in which an electronic ink is used as a material and the electronic ink is printed, thereby constituting the display device.
As shown in FIG. 9, an electronic ink is such a product that an microcapsule 906 having a diameter of about 80 μm is made, in which a transparent liquid, a white particle 901 positively charged and a black particle 902 negatively charged are encapsulated. When the electric field is impressed on the microcapsule 906, the white particle 901 and the black particle 902 are moved in a contrary direction. As shown in FIG. 9, the electric field is positively or negatively impressed between a counter-electrode (transparent electrode) 903 and pixel electrodes 904, 905, the white or black particle appears on the surface, and the white or black color is displayed. As for this electronic ink and the counter-electrode (transparent electrode), films are capable of being formed by a printing method, and an electrophoresis display device is a device that an electronic ink is printed on a circuit substrate.
An electrophoresis display device using an electronic ink has a merit that it consumes less electric power comparing to a liquid crystal device. First, it is since it has around 30% of the reflectance, and has several-fold of reflectance comparing to that of a reflection type liquid crystal. Since a reflection type liquid crystal has a lower reflectance, although it is advantageous at the place where the light is intense, for example, under the sun, at the place where the light is less intense, it is necessary to provide an auxiliary illumination such as a front light or the like. To the contrary, in the case of an electrophoresis display device using an electronic ink, since its reflectance is high, the front light is not needed. As for a front light, several hundreds mW of power is required, however, this power is not required for the device. Moreover, since liquid crystal uses an organic material, if the direct current drive is continued, the deterioration phenomenon will occur. Therefore, the alternating current inversion drive is needed, if the inversion frequency is low, a flicker is visibly recognized, it makes the user feel uncomfortable, therefore, alternating current inversion drive is normally carried out at 60-100 Hz. In an electrophoresis display device, it is not necessary to carry out the alternating current inversion drive as in a liquid crystal, accordingly, it is neither necessary to write at 60 Hz at each time. Owing to the two points described above, a low power consumption is capable of being realized.
E Ink Corp. has published an electrophoresis display device using amorphous silicon (a-Si) TFT in SID'01 DIGEST, p.152-155.
An electrophoresis display device using a-Si TFT is shown in FIG. 11. On the periphery of a pixel section 1100, it has source signal line drive circuits 1101, 1102 and a gate signal line drive circuit 1103 which has been externally mounted and supplied in a form of package such as IC or the like. The respective pixel is consisted of a source signal line 1104, a gate signal line 1105, a pixel TFT 1106, a pixel electrode 1107, a retention capacitor 1108 and the like.
FIG. 10 is a sectional view of a pixel after a microcapsule 1004 which is to be an electronic ink, and a counter-electrode 1001 have been formed, the operation of the particle in the microcapsule 1004 is controlled by the potential of the pixel electrode 1005, and the white or black color is displayed.
As described above, in the conventional electrophoresis display device, since a drive circuit is externally mounted, there have been problems from the viewpoints of cost, size of frame, reliability of terminal connection and the like.
Moreover, in the case where an electrophoresis display device is configured by employing a TFT substrate for amorphous, in order to retain the potential applied to the pixel electrode, the writing corresponding to the time constant determined by the retention capacitance of the pixel and off-state current of the pixel TFT has to be carried out. As for this, it is not required to write at 60 Hz as in employing the countermeasure for flicker, however, it requires refresh writing in a cycle of a certain length. Hence, in order to reduce the power consumption, a novel electrophoresis display device which is not required to write unless the picture is changed is needed.